EXPERIENCE WITH SUPERPAVE MIXES IN TEXAS. 88 th Annual Transportation Short Course Paul Hoelscher

Transcription

1 EXPERIENCE WITH SUPERPAVE MIXES IN TEXAS 88 th Annual Transportation Short Course Paul Hoelscher

2 Table of Contents 1 Why Use Superpave Mixes Initial Implementation and Results Adjusted Implementation Plan and Results Future Plan 25 5 Constructability Issues

3 Kent Stonewall Haskell Borden Scurry Fisher Jones ABILENE Howard Mitchell Nolan Taylor Callahan ABILENE DISTRICT

4 SuperPave Mixtures Why the Abilene District Transitioned from Conventional Mixes to Superpave Mixes??? Desire to improve performance life Higher Asphalt Content Stone on Stone Contact Typical Use Versatile mix used for a variety of applications ranging from high volume to low volume roadways; from new construction to overlays. Used as base, intermediate and surface layers. Advantages Can be used on medium to high volume roadways. The binder content can be adjusted by adjusting the N-des level. Stone on stone contact 4

5 Binder Content - Statewide Averages Mix Type Dense-Graded SuperPave Type A Type B Type C Type D

6 Average Mix Cost $86.40 $ / Ton $ Dense Graded SuperPave 6

7 SuperPave Mixtures History of Superpave Usage in the Abilene District Began Transition in early 2000 s Initially used SP-A base mix and SP-C surface mix Initially used a N-des level of gyrations Utilized several grades of asphalt in the SP-C (PG70-22 & PG76-22) Utilized PG64-22 in the base course Early Results SP-A very course and appeared to be open to water intrusion. Observed wet spots in SP-C surfaces the day after it rained. Little or no improvement in asphalt contents (AC) Compaction issues due to low AC Observed premature cracking with gyration mixes and/or PG

8 Built In 2003 US 84, Nolan Co. SP-C, PG76-22

9 Built In 2003 FM 89, Abilene TX SP-C, PG76-22

10 Built In 2003 SH 350, Snyder TX SP-C, PG70-22

11 Built In 2004 US 180, Roby TX SP-C, PG70-22

12 Built In 2004 FM 707, Taylor Co. SP-C, PG76-22

13 SuperPave Mixtures Implemented Changes to Achieve Desired Results New specification with the 2004 Spec Book Migrated from SP-A to SP-B base course Started trying SP-D surface mixes Reduced the N-des level to 75 gyrations Only used PG70-22 in surface mixes Continued to utilize PG64-22 in the base course Results SP-B less course and appeared to be less susceptible to water intrusion. SP-C mixes had better compaction properties resulting in less water intrusion. SP-D mixes appeared to be tighter and less susceptible to water intrusion. Observed an increase asphalt content with 75 gyration mix designs. 13

14 Binder Content - Statewide Averages Mix Type Dense-Graded SuperPave Type A Type B Type C Type D

15 Binder Content Abilene District Mix Type SuperPave Typical AC SP-B 4.7 SP-C 5.2 SP-D

16 Built In 2005 SH 70, Nolan Co SP-C, PG70-22

17 Built In 2005 BI 20-M, Sweetwater TX SP-C, PG70-22

18 Built In 2005 US 83, Stonewall Co. SP-D, PG70-22

19 Built In 2006 BU 83-D, Abilene TX SP-C, PG70-22

20 Built In 2006 SH 36, Abilene TX SP-C, PG70-22

21 Built In 2006 US 83, Jones Co SP-D, PG70-22

22 Built In 2007 FM 617, Haskell Co. SP-D, PG70-22

23 Built In 2007 US 380, Haskell TX SP-D, PG70-22

24 Built In 2008 US 87, Big Spring TX SP-D, PG70-22

25 SuperPave Mixtures 10 Year Performance History Performance overall is good. Very little or no rutting observed. Mix still appears to be too dry. Minor cracking occurs too early in the pavement life. Implementing Additional Changes to Achieve Better Results New specification with the 2014 Spec Book Reducing the N-des level to 50 gyrations Use more SP-C mixes 25

26 SuperPave Mixtures Constructability Issues More difficult to compact. May have intermediate temperature tenderness (tender-zone). 26

27 Issues Encountered Tender Zone During Compaction A temperature range during the cooling process of the mat in which the mix becomes tender. Excessive rolling in the Tender Zone can cause mat to shove and crack 27

28 SuperPave Mixtures Possible Causes of Tender-Zone Issues Placement on a smooth surface Improper roller frequency and/or amplitude Placement too thick for the mix type Percent fines too high (especially field sand) Primary Impact Will affect ride quality if not controlled Can leave rips and tears in the final mat Ways to Address Tender-Zone Issues Design to avoid placement on smooth surfaces Adjust roller frequency and amplitude Avoid rolling the mix in the temperature range where the mix is unstable during compaction Ensure adequate tacking is achieved Redesign 28

29 Questions? 29